Composite production with continuous metal and ceramic phases

ABSTRACT

The present invention relates to a ceramic alloy composite composition having the alloy spontaneously infiltrated into the ceramic, with the preferred ceramic alloy composite composition being a Si 3  N 4  /TiN/Cu-Ti composite composition and a method for forming the ceramic alloy composite composition.

TECHNICAL FIELD

The present invention relates to a method for the production ofcontinuous phase composite compositions having a continuous phase metaland a continuous phase ceramic and the compositions produced from themethod. The present invention preferably relates to a silicon nitride(Si₃ N₄) copper (Cu) titanium (Ti) composite composition (Si₃ N₄/Cu/Ti), more specifically to a (Si₃ N₄ /TiN/Cu-Ti) compositecomposition, and a method for forming such composite composition.

BACKGROUND ART

Composite materials comprised of alloy and ceramic materials are knownand are ideally suited for use in products requiring high temperaturetolerance and wear resistance, which is typically associated withceramics, and toughness, which is typically associated with metals oralloys. As such, the composite materials provide desirable wear,thermal, and hardness characteristics to products made from suchmaterials. When products are made from only a ceramic or only an alloythe products often lack the necessary combination of characteristicsrequired for certain uses. For instance, steel alloys have been used toform a variety of products, but the use of steel has been undesiredbecause it often does not impart sufficient thermal resistance for usein certain types of products. Ceramics impart high thermal resistance,but are generally not strong enough and do not have a high fracturetoughness. For these reasons composites are desirable because theycombine the desirable characteristics of both alloys and ceramics.

Engine components, such as valve guides and mechanical seals forexample, are subject to high temperature environments and are alsosubject to harsh conditions which test the strength and wear resistanceof the components. For these types of components it is desired to use acomposite material comprised of an alloy or metal and a ceramic becauseof the desired combined characteristics. Specifically, the mentionedengine components require high temperature tolerance and increasedhardness and wear resistance characteristics, so that the componentsrequire the characteristics associated with the alloys and the ceramics.

The composite compositions, however, have typically not been used toform the above-mentioned types of components and devices because theprocess for forming products from such composite compositions hasgenerally been too expensive. Hot isostatic pressing is an example of amethod that has been previously used to produce ceramic alloy compositecompositions. Unfortunately, hot isostatic pressing is currently anexpensive process to perform and the composite compositions have to beproduced and then machined into a finished product. Machining compositecompositions into a finished component or product is generallyexpensive. For these reasons, it is desired to have a process, otherthan hot isostatic pressing, for producing composite compositions. It isfurther desired to have a process for forming composite compositionswhich is presently not economically prohibitive and which is suited foruse in the production of various engine components. Additionally, it isdesired to have a process for forming composite compositions which doesnot require extensive machining of products made from the compositematerials, but which instead allows for the production of the componentduring formation of the composite composition. In other words, it isdesired to form a ceramic of the desired component shape and then formthe composite composition.

DISCLOSURE OF THE INVENTION

The present invention relates to a method for forming a continuous phasecomposite composition and the continuous phase composite compositionformed from the method. The composite composition will be comprised ofan alloy and a ceramic substrate, with the alloy spontaneouslyinfiltrated into the ceramic substrate. Preferably, the continuous phasecomposite composition will be comprised of an Si₃ N₄ substrate, atitanium-nitride layer, and a copper titanium alloy layer, so that anSi₃ N₄ /TiN/Cu-Ti composite composition is formed.

The method includes the steps of press forming a ceramic into a ceramicsubstrate, firing the ceramic substrate to form a fired ceramicsubstrate, and spontaneously infiltrating the fired ceramic substratewith an alloy. First, a ceramic is chosen to form the ceramic substrate.The ceramic is preferably a ceramic nitride and more preferably isselected from the group consisting of alumina, aluminum nitride, siliconnitride, and combinations thereof. Once selected, the ceramic is formpressed into a ceramic substrate having a density ranging between about40% and about 50%. It is preferred if the ceramic is form pressed into ashape resembling the finished product.

Next the ceramic substrate is fired to further densify the ceramic. Anyof a variety of methods can be used to fire the ceramic so long as theceramic has a porosity ranging between about 10% and about 50%. Theporosity will determine whether the composite composition hascharacteristics more similar to the alloy or the ceramic.

The fired ceramic substrate is then spontaneously infiltrated with analloy. Any of a variety of alloys can be used as long as the alloycontains either titanium or chromium in an amount equal to up to 50% byweight of the alloy. A variety of methods can be used to heat the alloyso long as the alloy is spontaneously infiltrated into the ceramicsubstrate.

After performance of the method a continuous phase composite compositionwill be formed. Preferably, the present method will result in theformation of a Si₃ N₄ /TiN/Cu-Ti composite composition.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention relates to a ceramic metal continuous phasecomposite composition and a method for producing the continuous phasecomposite composition, with the composite composition comprised of acontinuous metal phase and a continuous ceramic phase. Preferably, a Si₃N₄ /TiN/Cu-Ti composite composition is formed wherein the compositesystem has a silicon nitride (Si₃ N₄) substrate, a titanium nitride(TiN) layer, and a copper-titanium (Cu-Ti) alloy layer, with the alloyspontaneously infiltrated into the substrate. The composite compositionis well suited for use in the production of high temperature tolerantand impact resistant structural components such as engine components.

The method is initiated by selecting a ceramic for use as a substrate,with any ceramic available for use that has a constituent that willreact with an alloy to form a bond between the alloy and the ceramic.More particularly, the ceramic should allow for spontaneous infiltrationof the alloy into the ceramic substrate. Generally, any ceramic nitridecan be used as the ceramic substrate material. Preferably, the ceramicsubstrate material is selected from the group consisting of siliconnitride (Si₃ N₄), aluminum nitride (AlN), alumina (Al₂ O₃), andcombinations thereof. The most preferred ceramic for use as thesubstrate is Si₃ N₄. It is also preferred if the substrate material isin powder form so it can be readily shaped into a product.

Once the ceramic has been selected it is form processed so that theceramic, preferably Si₃ N₄, is formed into a substrate having a shaperesembling the desired finished product. The forming process for the Si₃N₄ substrate involves compressing the ceramic to form a pressed ceramicsubstrate having a density ranging between about 40% and about 50%.Typically, a dry pressing method is used to form the pressed ceramicsubstrate; however, any method can be used that forms the pressedceramic material into a substrate having a density ranging between about40% and about 50%. Among the methods available for form processing theceramic material into the pressed ceramic substrate are dry-pressing,isostatic pressing, slip casting, gel casting, injection molding, andfree-form fabrication.

After formation of the pressed ceramic substrate, the substrate is firedto further densify the ceramic material and form a fired ceramicsubstrate. The particular time and temperature used to fire the ceramicsubstrate will be dependent upon the desired density and grain size ofthe finished ceramic substrate. If the composite composition requirescharacteristics typically associated with the ceramic, then it isnecessary to process the ceramic longer to increase the density anddecrease the porosity. If the composite composition requirescharacteristics more typically associated with an alloy or metal than itis necessary to process the ceramic a lesser amount of time. Porosity,which is directly related to density, in the ceramic can range betweenabout 10% and about 50%, with the lesser porosity the result of highertemperatures and longer processing times. Also, with increasedtemperature and time the grain size in the ceramic will increase. As theporosity decreases less alloy can infiltrate the substrate and, as such,the composite composition will be characterized more by the ceramic thanby the alloy. The firing step will form a solid fired ceramic substrate,with the heating or firing of the ceramic achieved in a number of ways.Among the methods available for firing the ceramic are conventionalsintering, microwave sintering, hot isostatic pressing, and plasma arcsintering.

Conventional sintering or heating in a box furnace in air is the mostpreferred way for firing the pressed ceramic substrate. The ceramic istypically processed by firing the Si₃ N₄ at a temperature rangingbetween about 1000° C. and about 1200° C. for a time period rangingbetween about 30 minutes and about five (5) hours. More preferably, thepressed ceramic substrate is fired for a period of time ranging betweenabout 60 minutes and about 120 minutes.

Following the ceramic, preferably Si₃ N₄, substrate formation, thesubstrate is spontaneously infiltrated with an amount of an alloy ormetal. Any alloy or metal can be used that contains a constituent thatwill react with and spontaneously infiltrate the ceramic substrate. Thereaction that occurs should provide for wetting of the alloy into thesubstrate, so as to allow the ceramic to be spontaneously infiltrated.Among the alloys suitable for use in the present invention are coppertitanium (Cu-Ti), nickel-titanium (Ni-Ti), iron-titanium (Fe-Ti), alloysof titanium, chromium (Cr) alloys of nickel, titanium (Ti), and copper,and titanium alloys of nickel, iron, and copper, with all of the alloyshaving up to 50% by weight of Ti or Cr. Preferably, a copper-titaniumalloy (Cu-Ti) is infiltrated into the Si₃ N₄ substrate to form a Si₃ N₄/TiN/Cu-Ti composite composition. The infiltration of the Cu-Ti alloyinto the substrate will occur at a temperature ranging between about1000° C. and about 1200° C. for a period of time equal to between about30 minutes and about 120 minutes. It is also preferred if theinfiltration occurs in a vacuum or in a reducing atmosphere containingapproximately 5% H₂ and with the balance being Argon. The atmosphereshould be devoid of oxygen to prevent oxidation of the alloy. Anycontrolled atmosphere furnace can be used to infiltrate the alloy intothe ceramic substrate. Any amount of time can be used for infiltratingthe alloy into the substrate, so long as the alloy is sufficientlymelted; however, preferably, the time for melting the alloy will beequal to about 60 minutes.

The alloy prior to infiltration into the substrate and densification canbe in powdered form, melted liquid form, sheet form, or ingot form. Anyform can be used as long as the alloy is spontaneously infiltrated intothe ceramic substrate and the composite composition is formed. Methodsfor heating the powder alloy include placing the substrate alloy powdercombination in a hot press devoid of oxygen.

The finished composite composition will have an amount of ceramic equalto from about 50% to about 90% by volume of the composite compositionand an amount of alloy equal to from about 50% to about 10% by volume ofthe composite composition. The preferred composite composition will havethe formula Si₃ N₄ /TiN/Cu-Ti.

EXAMPLES

A composite composition was formed by first dry pressing 2.0 gms of Si₃N₄ powder (Stock #SN-E10, UBQ 050002, Ube Inc., 2-3-11,Higashi-Shinagawa, Shingawa-Ku, Tokyo, Japan) without a binder in adouble acting steel die, at a pressure of 5200 psi. The Si₃ N₄ powderwas pressed into a pellet shape. Stearic acid was used as the dielubricant. The dry pressing step formed a pressed Si₃ N₄ substratepellet.

The pressed Si₃ N₄ substrate was then fired in air in a box furnace(Model #26144, Lindberg, A Unit of General Signal, Watertown, Wis.53094) for 3 hours at 1200° C. The density of the pellet after firing,as measured by Archimdes method, was 47.6% of theoretical, or 1.52gm/cc. The firing step resulted in the formation of a fired Si₃ N₄substrate pellet.

An alloy powder in an amount equal to 2.1 gms and having thecomposition, 50% by weight Cu (Cu Stock #A16234, Alfa Aesar, Wardhill,Mass.) and 50% by weight of Ti, (Ti stock #10386, Alfa Aesar, Wardhill,Mass.) was placed on the fired Si₃ N₄ substrate in a vacuum hot-press(Model #VHP-12-12-12-2100 100T, AVS Inc., 60 Fitchburg Rd., Ayer, Mass.01432) without applying any mechanical load. The base pressure of therun was 10 mTorr. The sample was fired at 1000° C. for 1 hour. At theconclusion of firing a Si₃ N₄ /TiN/Cu-Ti composite composition wasformed.

INDUSTRIAL APPLICABILITY

The present invention relates to a method for forming a compositecomposition preferably of the formula Si₃ N₄ /TiN/Cu-Ti and thecomposition. Composite compositions are often used to form componentsand devices used in engines, for example. It is desired to have acomposite composition for use in forming components and devices, as thecomposite compositions ideally impart high temperature tolerance andwear resistance. In particular, the Si₃ N₄ /TiN/Cu-Ti compositecomposition is well suited for use in applications requiring hightemperature tolerance and wear resistance. As such, the Si₃ N₄/TiN/Cu-Ti composite composition is useful in forming various componentsand parts, especially engine components.

It is also desired to have a method for making this compositecomposition that is presently cost effective and easily forms thecomposite composition. The present method is a cost effective method forforming the composite composition and results in the formation ofcomposite compositions having high temperature tolerance and wearresistance.

What is claimed is:
 1. A method for forming a ceramic alloy compositecomposition wherein the steps of said method are:a) pressing a ceramicto form a pressed ceramic substrate having a density ranging betweenabout 40% and about 50%; b) firing said pressed ceramic substrate at atemperature ranging between about 1000° C. and about 1200° C. for aperiod of time ranging between about 30 minutes and about five hours toform a ceramic substrate; and, c) spontaneously infiltrating saidceramic substrate with an amount of an alloy capable of spontaneouslyinfiltrating said ceramic substrate and containing a constituent thatwill allow wetting of said alloy on said ceramic substrate, with saidspontaneous infiltration step performed at a temperature ranging betweenabout 1000° C. and about 1200 C. for a period of time ranging betweenabout 30 minutes and about 120 minutes, with said method forming saidceramic alloy composite composition.
 2. The method of claim 1 whereinsaid ceramic is selected from the group consisting of ceramic nitrides.3. The method of claim 2 wherein said ceramic is selected from the groupconsisting of silicon nitride, aluminum nitride, alumina, andcombinations thereof.
 4. The method of claim 3 wherein said ceramic ispreferably selected from the group consisting of Si₃ N₄.
 5. The methodof claim 1 wherein said alloy is selected from the group consisting oftitanium alloys and chromium alloys.
 6. The method of claim 5 whereinsaid alloy is selected from the group consisting of copper titanium,nickel titanium, iron titanium, alloys of titanium, chromium alloys ofnickel, titanium, and copper, and titanium alloys of nickel, iron, andcopper.
 7. The method of claim 1 wherein said ceramic substrate has aporosity ranging between about 10% and about 50%.
 8. The method of claim1 wherein said spontaneous infiltration step occurs in an atmospheresubstantially devoid of oxygen.
 9. A method for forming a Si₃ N₄/TiN/Cu-Ti composite composition wherein the steps of said method are:a)pressing an amount of Si₃ N₄ powder into a pressed Si₃ N₄ substratehaving density equal to between about 40% and about 50%; b) firing saidpressed Si₃ N₄ substrate at a temperature ranging between about 1000° C.and about 1200° C. for a period of time ranging between about 30 minutesand about five hours to form a fired Si₃ N₄ substrate having a porosityranging between about 10% and about 50%; and, c) infiltrating said firedSi₃ N₄ substrate with a Cu-Ti alloy at a temperature ranging between1000° C. and 1200° C. for a time period ranging between about 30 minutesand 120 minutes in a non-oxidizing atmosphere to form said Si₃ N₄/TiN/Cu-Ti composite composition.
 10. The method of claim 9 wherein saidSi₃ N₄ /TiN/Cu-Ti composite composition is comprised of an amount of Si₃N₄ equal to from about 50% to about 90% by volume of said Si₃ N₄/TiN/Cu-Ti composite composition and an amount of Cu-Ti alloy equal tofrom about 50% to about 10% by volume of said Si₃ N₄ /TiN/Cu-Ticomposite composition.
 11. A ceramic alloy composite composition havingan amount of alloy equal to from about 50% to about 10% by volume ofsaid composite composition and an amount of ceramic equal to from about50% to about 90% by volume of said composite composition, with saidceramic having a porosity ranging between about 10% and about 50%. 12.The composite composition of claim 11 wherein said ceramic is selectedfrom the group consisting of ceramic nitrides.
 13. The compositecomposition of claim 12 wherein said ceramic is selected from the groupconsisting of silicon nitride, aluminum nitride, alumina, andcombinations thereof.
 14. The composite composition of claim 13 whereinsaid ceramic is Si₃ N₄.
 15. The composite composition of claim 11wherein said alloy is selected from the group consisting of titaniumalloys and chromium alloys.
 16. The composite composition of claim 15wherein said alloy is selected from the group consisting of coppertitanium, nickel titanium, iron titanium, alloys of titanium, chromiumalloys of nickel, titanium, and copper, and titanium alloys of nickel,iron, and copper.